1. Technical Field
Techniques for production of metallic nickel and cobalt.
2. Description of Related Art
Nickel and cobalt have traditionally been recovered from sulfide and oxide sources by both pyrometallurgical and hydrometallurgical techniques, with pyrometallurgical processing usually applied to the source feed (ore or concentrate) and hydrometallurgical methods employed for the final steps of metal refining. Trends over the last 10-15 years have witnessed increased application of hydrometallurgical technologies for direct treating of the source nickel/cobalt containing feeds. These would typically begin with an acid leach, followed by solution purification steps leading to the production of intermediates hydroxides, sulfides, carbonates), which would be further hydrometallurgically refined as required, or to the production of final metal products by electrowinning.
More recent developments have demonstrated the application of pyrometallurgical processes to refined hydrometallurgical solutions or intermediates for the production of the final product. Pyrometallurgical techniques typically involve drying, calcining/reduction and electric furnace smelting which produces ferro-nickel or nickel sulphide matte, which may be further processed to recover purified nickel. Pyrometallurgical techniques are usually applied to saprolite. Hydrometallurgical techniques are more typically applied to limonitic laterites. These techniques include the Caron process, high-pressure acid leaching (HPAL) with sulfuric acid at high temperature and high pressure, and atmospheric leaching, e.g., heap leaching with sulfuric acid at atmospheric temperature and pressure. Following leaching, the leachate is suitably neutralized to remove impurities such as Fe and Al, which is then followed by precipitation of a mixed Ni/Co intermediate, such as hydroxide, carbonate or sulphide, or the solution is subjected to solvent extraction or ion-exchange for the further removal of impurities (such as manganese) and/or the separation of nickel from cobalt. Nickel hydroxide may be produced from acidic nickel sulfate solutions produced as eluates, strip solutions, or raffinates from solvent extraction or ion exchange treatment. Nickel hydroxide may be subject to further processing and, e.g., be transformed into nickel oxide. Care must be taken in the handling of nickel oxide because nickel oxide powder is known to be hazardous.
WO 2006/089358 describes a process for the production of ferronickel from a mixed nickel iron hydroxide product which includes providing a mixed nickel iron hydroxide product; pelletizing the mixed nickel iron hydroxide product to produce nickel iron hydroxide pellets; calcining the nickel iron hydroxide pellets to produce mixed nickel iron oxide pellets; and reducing the nickel iron oxide pellets with one or more reducing gases at high temperatures to produce ferronickel pellets. As described therein, the mixed nickel iron hydroxide product would generally be in the form of a wet cake and to pelletize the mixed nickel iron hydroxide product, the wet cake is dried and pelletized with an organic binding material and water. Organic binding materials discussed therein are “a cellulose solution, starch or other viscous organic hydrocarbon polymers which are destroyed when temperatures exceed 500° C.” The pelletized nickel iron hydroxide product is first dried at a temperature of about 100° C.-120° C. and then calcined at temperatures of about 800° C.-1300° C. under oxidizing conditions to convert the nickel iron hydroxide pellets to nickel iron oxide pellets substantially free of sulfur. At page 11, it is stated that the metals in the product from the furnace are mainly in the form of trevorite, a complex nickel iron oxide NiFe2O4 and the product is in the form of porous pellets. The porous pellets are not friable and no extraordinary measures are necessary to prevent formation of a hazardous powder. Use of bentonite as a binder in connection with production of iron is known. See also, WO 2008/022381 which is directed to production of metallic nickel with low iron content. The application does not disclose any techniques for controlling or eliminating the potential for hazardous nickel oxide powder.